The present invention relates to closure and container combinations, and more particularly, to closures which utilize the internal pressure of the container contents to effect a seal.
Due to cost and safety considerations, it is desirable to fabricate carbonated beverage containers from polyethylene terephthalate (PET). Containers for carbonated beverages made from PET are blow molded in mass quantities from preforms. An advantage of using PET is that it is easily recyclable. However, with present designs, the carbonated beverage container itself is made of PET and includes a threaded mouth which receives a cap made of aluminum. The aluminum closure or cap includes a ring of perforations which forms a line of separation so that, when removed from the container, the cap leaves behind a thin aluminum ring.
Accordingly, at some point in the recycling process, it is necessary to separate the aluminum ring from the PET material. This separation step would be eliminated if the entire container-closure combination could be made of PET. Since PET has a different strength than aluminum, it is necessary to design a different closure shape. One example of such a closure and container is disclosed in Wiedmer U.S. Pat. No. 3,825,144. That patent discloses a container closure for sealing bottles having pressurized contents and includes a sealing member having a deformable disk portion with an outwardly concave shape. The disk portion deforms in response to the internal pressure of the container contents. However, such a flexible closure is unsuitable for fabrication of PET, since the internal pressure of a typical carbonated beverage container is not sufficiently great to deform the entire surface of such a closure.
Accordingly, there is a need for a container and closure design suitable for a carbonated beverage in which the closure can be made of a flexible plastic material such as PET. Further, a disadvantage with such closures is that they lack means for the gradual release of pressure within the container. As a result, there is a risk that, when opening such a prior art closure, the closure is propelled from the container by the pressure from the contents within the container; or that the gaseous contents of the container. Accordingly, there is a need for a container and closure mechanism in which the internal pressure generated by the contents of the container effects a seal and in which means are provided for the gradual equalization of pressure within the container during opening of the closure.